Lana originated as a tropical depression in the extreme western portion of the east Pacific basin, and became a short-lived tropical storm in the central Pacific basin before moving well south of the Hawaiian Islands and dissipating.

a. Synoptic History

Lana had its origins in a tropical wave that entered the eastern Atlantic on 11 July and reached the eastern Pacific on 21 July. The area of disturbed weather associated with the wave merged with another area of disturbed weather on 26 July, and by 0000 UTC 27 July the system was located near 115-120°W. As the system moved westward, vertical wind shear remained unfavorable for development for a couple of days, but shear began to decrease on 29 July as a mid- to upper-level trough located north of the wave moved away. Deep convection began to increase late on 29 July and the system continued to become better organized early on 30 July. It is estimated that a tropical depression formed around 1200 UTC 30 July while centered about 1030 n mi east-southeast of Hilo, Hawaii. The "best track" chart of the tropical cyclone's path is given in Fig. 1, with the wind and pressure histories shown in Figs. 2 and 3, respectively. The best track positions and intensities are listed in Table 1[1].

The depression moved quickly westward at 16-17 kt to the south of the subtropical ridge, and the convective structure of the cyclone continued to become better organized. It crossed 140°W longitude and entered the central Pacific basin just prior to reaching tropical storm intensity around 1800 UTC 30 July, when it was centered about 935 n mi east-southeast of Hilo. Steady strengthening beneath upper-level anticyclonic flow continued for the next 24 h, and by 1800 UTC the next day Lana reached its peak intensity of 55 kt while located about 585 n mi southeast of Hilo. Increasing southwesterly vertical wind shear began to impinge upon the cyclone as it approached an upper-level trough over Hawaii, and Lana gradually weakened during the following two days as it continued westward in the low- to mid-level flow south of a ridge. By 1800 UTC 2 August, Lana had weakened to a tropical depression about 400 n mi south of Honolulu, Hawaii. Thereafter, only small, intermittent bursts of convection appeared in the northeastern quadrant, and the system degenerated to a remnant low six hours later. The low dissipated in the low-level trade wind flow shortly after 0600 UTC 3 August about 475 n mi southwest of Honolulu.

b. Meteorological Statistics

Observations in Lana (Figs. 2 and 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Central Pacific Hurricane Center (PHFO), and the Satellite Analysis Branch (SAB). Data and imagery from NOAA polar-orbiting satellites, the NASA Tropical Rainfall Measuring Mission (TRMM), the NASA QuikSCAT, the European ASCAT onboard METOP-A, and Defense Meteorological Satellite Program (DMSP) satellites, among others, were also useful in constructing the best track of Lana.

Lana's estimated peak intensity of 55 kt on 31 July is based upon subjective Dvorak intensity estimates of 55 kt from both SAB and PHFO at 1800 UTC that day (Fig. 2).

No ship reports of winds of tropical storm force were reported in association with Lana.

c. Casualty and Damage Statistics

There were no reports of damage or casualties associated with Lana.

d. Forecast and Warning Critique

The genesis of Lana was not well anticipated. The precursor disturbance that developed into Lana was first mentioned in NHC's Tropical Weather Outlook issued at 1800 UTC 27 July, and was given a "low" probability of genesis (less than 30%) in the next 48 h. The genesis forecast remained in the low category through 1800 UTC 28 July. Due to increasing vertical wind shear, the disturbance was removed from the outlook at 0000 UTC 29 July. After the shear diminished later that day, the disturbance was again given a low probability of genesis. The probability of formation remained in the low category until genesis occurred.

NHC made only one forecast for Lana, which prevents any meaningful forecast critique. Official track forecast errors were 38, 75, 93, 86, and 85 n mi for the 12, 24, 36, 48, and 72 h forecasts, respectively. Official intensity forecast errors were 10 kt at 12 and 24 h, and 0 kt at 36, 48, and 72 h.

No coastal tropical cyclone watches or warnings were issued in association with Lana.

[1] A digital record of the complete best track, including wind radii, can be found on line at ftp://ftp.nhc.noaa.gov/atcf. Data for the current year's storms are located in the btk directory, while previous years' data are located in the archive directory.

Tropical Cyclone Report
Hurricane Felicia
(EP082009)
3-11 August 2009

Todd B. Kimberlain
National Hurricane Center

Derek Wroe and Richard D. Knabb
Central Pacific Hurricane Center

14 January 2010

Felicia strengthened into a major hurricane over the western portion of the eastern North Pacific basin. The hurricane gradually weakened over the central Pacific, and dissipated just east of the Hawaiian Islands.

a. Synoptic History

Felicia's genesis can be traced to a tropical wave that was first detected in satellite imagery over the tropical Atlantic on 23 July. The wave was barely identifiable for several days but became better defined as it approached the Lesser Antilles on 26 July. Little change in the wave was noted as it passed through the Caribbean Sea and moved across Central America during the last few days of July. Scattered deep convection began to develop in association with the wave after it moved into the eastern North Pacific on 29 July, but it was not until the wave passed 110°W on 1 August that deep convection increased further and showed signs of organization. Satellite images indicated several curved bands on 3 August around a developing circulation center, and the disturbance is estimated to have become a tropical depression by 1800 UTC 3 August. Additional organization occurred and the depression became a tropical storm around 0000 UTC 4 August, centered about 990 n mi southwest of the southern tip of Baja California. The "best track" chart of the tropical cyclone's path is given in Fig. 1, with the wind and pressure histories shown in Figs. 2 and 3, respectively. The best track positions and intensities are listed in Table 1[1].

Within an environment of low vertical wind shear and 28°-29°C sea surface temperatures, Felicia began a period of rapid intensification from the time it formed. A NASA Tropical Rainfall Measuring Mission (TRMM) 85-GHz microwave pass at 1327 UTC 4 August captured Felicia in the middle of this intensification phase, revealing a well-defined mid-level eye-like feature within a central dense overcast (Fig. 4). Microwave imagery and Dvorak satellite estimates suggest that Felicia continued to rapidly intensify and reached hurricane strength around 1800 UTC 4 August.

Felicia initially moved west-northwestward between 12 and 14 kt to the south of a well-defined deep-layer ridge covering the central portion of the eastern North Pacific. However, Felicia slowed to a forward speed of 9 to 10 kt and started moving on a more northwestward heading by 5 August, when it reached the western extent of a ridge to its north and encountered a trough digging along 130°W. The cyclone may have also been involved in a weak binary interaction with Tropical Storm Enrique to its northeast during its developing stage, with the separation distance between the two as little as 425 n mi around 1200 UTC 6 August. Despite their proximity, the tracks of the two cyclones indicate that whatever interaction occurred was minimal.

On a northwestward course, Felicia continued to rapidly intensify and reached its estimated peak intensity of 125 kt at 0600 UTC 6 August, while located about 1465 n mi east-southeast of Hilo, Hawaii. Although the environmental shear remained fairly light, gradual weakening began during the next 24 hours, followed by a faster weakening after Felicia began moving over 26° to 27°C sea surface temperatures. Around this time, mid-level ridging building to the north and west of the hurricane replaced the mid- to upper-tropospheric trough that was along 130°W. The change in steering features resulted in a more west-northwesterly course just prior to Felicia's entrance into the central North Pacific basin a hurricane with 80 kt winds around 1200 UTC 8 August.

Early on 9 August, aircraft reconnaissance data and microwave imagery indicated that the flight-level center was no longer collocated with the surface center. This marked the beginning of a weakening trend, as Felicia encountered increasing westerly vertical wind shear produced by a broad upper-level trough over and north of the Hawaiian islands. Felicia weakened to a tropical storm by 1200 UTC that day while centered about 550 n mi east of Hilo. By 0000 UTC 10 August, the shear had exacted a substantial toll on Felicia, as the low-level circulation center had become exposed from deep convection displaced to the northeast, and maximum winds had diminished to 45 kt, down from 75 kt just 24 hours earlier. As the tropical storm weakened, the dominant steering flow was a low- to mid-level subtropical ridge to the north, causing Felicia to assume a westward motion for the remainder of its existence.

Gradual weakening continued through 10 August in an environment of continued strong westerly shear. The upper-level trough responsible for the shear also created diffluence aloft, however, which helped to maintain an area of deep convection displaced to the north-northeast of the exposed low-level center. While this convection continued, aircraft reconnaissance and QuikSCAT data continued to indicate winds of tropical storm force to the north of the circulation center through early on 11 August. Later that day, the diffluent pattern aloft broke down, while vertical wind shear remained strong over the cyclone, and deep convection diminished. Felicia weakened to a tropical depression by 1200 UTC 11 August while centered 120 n mi northeast of Hilo, and became a remnant low around 1800 UTC. Shortly thereafter, the low-level circulation center became ill-defined as it interacted with the high terrain of the Big Island of Hawaii, and the circulation dissipated. Remnant moisture then continued westward over the rest of the Hawaiian Islands for the next couple of days.

b. Meteorological Statistics

Observations in Felicia (Figs. 2 and 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB) and the Satellite Analysis Branch (SAB), the Central Pacific Hurricane Center (CPHC), and the Joint Typhoon Warning Center (JTWC). Data and imagery from NOAA polar-orbiting satellites, including the Advanced Microwave Sounding Unit (AMSU) intensity estimates using the CIMSS technique, the NASA Tropical Rainfall Measuring Mission (TRMM), the NASA QuikSCAT, the NASA Aqua, the Department of Defense Windsat, and Defense Meteorological Satellite Program (DMSP) satellites, among others, were also useful in tracking Felicia and later constructing its best track.

Flight-level, dropsonde, and Stepped-Frequency Microwave Radiometer (SFMR) data were also obtained during five C-130J aircraft missions flown by the 53rd Weather Reconnaissance Squadron of the U.S. Air Force Reserve Command. The NOAA G-IV jet also flew three synoptic surveillance missions around Felicia during 7-9 August.

The estimated peak intensity of Felicia of 125 kt is based on several subjective Dvorak intensity estimates of 127 kt and a 3-hour Automated Dvorak Technique (ADT) mean of 6.5 (127 kt) at 0000 UTC 6 August. Several QuikSCAT passes were also helpful in estimating the tropical-storm-force wind radii of Felicia and its intensity as the cyclone approached Hawaii as a tropical storm.

No ship reports of tropical-storm-force winds or greater were received in association with Felicia.

While approaching the Hawaiian Islands from the east, Felicia generated large swells, resulting in surf heights of 6 to 10 ft that affected east-facing shores of the state during 10-12 August.

Although Felicia dissipated as a tropical cyclone before reaching the Hawaiian Islands, widespread heavy rainfall and some freshwater flooding occurred as the remnants of the system passed over the state during 11-13 August. A portion of Kamehameha Highway near Waikane on the island of Oahu was closed for several hours on 13 August, as Waikane Stream overflowed its banks and sent floodwaters over the road. The greatest rainfall totals associated with the remnants of Felicia were 14.63 in at Oahu Forecast National Wildlife Refuge on the island of Oahu, 13.46 in at Mount Waialeale on the island of Kauai, and 6.28 in at West Wailuaki on the island of Maui.

c. Casualty and Damage Statistics

There were no reports of damage or casualties associated with Felicia.

d. Forecast and Warning Critique

The genesis of Felicia was not well anticipated. The area of disturbed weather from which Felicia developed was introduced to the Tropical Weather Outlook about 30 h prior to the tropical cyclone's formation. The first several outlooks indicated slow development of the system but did not explicitly mention the possibility that a tropical depression could form until 18 hours before genesis occurred. The potential for genesis never reached the "high" category (> 50% in 48 h).

A verification of NHC official track forecasts is provided in Table 2b. Average official track errors for Felicia (with the number of cases in parentheses) were 22 (18), 38 (18), 51 (18), 63 (18), 75 (18), 91 (15), and 150 (11) n mi for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively. These errors are much lower than the long-term NHC average track errors, especially at 48 h and beyond. Interestingly, NHC forecasts exhibited skill above or rivaling the often difficult-to-beat variable consensus (TVCN) model through 72 h in Table 2b. Additionally, BAMD produced the lowest overall track errors for Felicia at all time ranges except 72 h. It is worth noting that OCD5 errors were also smaller than average, suggesting that the track of Felicia was easier to forecast than average. This may also help explain the small OFCL errors.

A verification of NHC official intensity forecasts are shown in Table 3b. The average official intensity errors were 8 (18), 14 (18), 18 (18), 19 (18), 12 (18), 9 (15) and 10 (11) kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively. For comparison, the average long-term official intensity errors are 6, 10, 13, 15, 18, 19, and 19 kt, respectively. NHC forecast intensity errors were higher than the long-term average intensity errors through 48 h, revealing the inability of early forecasts to capture Felicia's period of rapid intensification starting at the time of genesis. It should be noted that none of the intensity guidance models for Felicia performed well through the 48 h time range. The large OCD5 errors at these time ranges indicate increased difficulty associated with these forecasts. Interestingly, NHC forecast intensity errors were substantially lower than the long-term average at 72 h and beyond, likely because they did not involve forecasting the initial rapid intensification phase.

Table 4 summarizes the tropical storm watches issued by the CPHC in association with Felicia.

Watches associated with Felicia are given in Table 4. A tropical storm watch was issued at 0300 UTC 9 August for the islands of Hawaii, Maui, Molokai, Lanai, and Kahoolawe and was expanded to cover the island of Oahu at 0300 UTC 10 August. Felicia dissipated before reaching the Hawaiian Islands, and no warnings were issued.

Table 1. Best track for Hurricane Felicia, 3-11 August 2009.

Date/Time(UTC)

Latitude(°N)

Longitude(°W)

Pressure(mb)

Wind Speed(kt)

Stage

03 / 1800

11.0

121.1

1007

25

tropical depression

04 / 0000

11.5

122.4

1004

35

tropical storm

04 / 0600

11.8

123.7

1000

45

"

04 / 1200

12.0

124.9

994

55

"

04 / 1800

12.2

126.1

987

65

hurricane

05 / 0000

12.6

126.9

980

75

"

05 / 0600

13.2

127.6

972

85

"

05 / 1200

13.7

128.5

960

100

"

05 / 1800

14.2

129.3

948

115

"

06 / 0000

14.7

130.1

935

125

"

06 / 0600

15.1

130.8

935

125

"

06 / 1200

15.7

131.5

940

120

"

06 / 1800

16.2

132.3

944

115

"

07 / 0000

16.7

133.2

948

115

"

07 / 0600

17.3

134.0

955

105

"

07 / 1200

17.7

135.2

960

100

"

07 / 1800

18.1

136.3

965

95

"

08 / 0000

18.6

137.4

970

90

"

08 / 0600

18.9

138.7

973

85

"

08 / 1200

19.2

140.1

976

80

"

08 / 1800

19.6

141.4

981

75

"

09 / 0000

19.9

142.7

982

75

"

09 / 0600

20.2

144.0

984

70

"

09 / 1200

20.5

145.3

994

60

tropical storm

09 / 1800

20.9

146.5

1001

50

"

10 / 0000

21.0

147.7

1002

45

"

10 / 0600

21.0

148.7

1003

45

"

10 / 1200

20.9

149.6

1005

40

"

10 / 1800

20.9

150.6

1007

40

"

11 / 0000

20.9

151.6

1008

35

"

11 / 0600

20.9

152.5

1009

35

"

11 / 1200

20.8

153.3

1010

30

tropical depression

11 / 1800

20.7

154.2

1010

30

low

12 / 0000

dissipated

06 / 0000

14.7

130.1

935

125

minimum pressure/maximum wind

Table 2a. NHC official (OFCL) and climatology-persistence skill baseline (OCD5) track forecast errors (n mi) for Hurricane Felicia. Mean errors for the five-year period 2004-8 are shown for comparison. Official errors that are smaller than the five-year means are shown in boldface type. * CPHC statistics are incomplete at this time, and will be provided as soon as possible.

Forecast Period (h)

12

24

36

48

72

96

120

OFCL (Felicia)

21.6

38.2

51.2

63.1

75.0

90.5

150.4

OCD5 (Felicia)

26.2

47.0

75.1

106.6

170.4

213.9

207.7

Forecasts

18

18

18

18

18

15

11

OFCL (2004-8)

31.0

51.7

71.7

90.2

123.6

161.3

201.8

OCD5 (2004-8)

38.4

73.6

111.9

149.1

214.2

261.1

311.5

Table 2b. Homogeneous comparison of selected track forecast guidance models (in n mi) for Hurricane Felicia east of 140°W. Errors smaller than the NHC official forecast are shown in boldface type. The number of official forecasts shown here will generally be smaller than that shown in Table 2a due to the homogeneity requirement.

Model ID

Forecast Period (h)

12

24

36

48

72

96

120

OFCL

18.9

36.3

49.1

60.9

71.8

89.8

149.5

OCD5

24.6

48.4

76.8

111.2

173.3

214.4

213.9

GFSI

25.8

41.9

51.8

61.0

72.2

120.6

178.8

GHMI

19.5

39.4

57.5

73.1

106.2

129.4

197.2

HWFI

26.1

48.9

62.9

78.8

113.5

150.0

200.8

NGPI

38.7

73.9

96.3

107.5

104.5

132.5

181.5

EMXI

22.3

44.4

62.2

79.4

97.2

93.3

122.4

TVCN

20.9

39.8

54.7

64.2

76.4

85.4

127.4

TVCC

21.1

44.3

57.3

77.3

92.3

122.7

174.5

BAMS

25.0

53.2

79.2

105.4

129.4

163.7

178.4

BAMM

20.9

38.3

56.7

83.9

140.7

165.0

147.0

BAMD

16.2

29.5

45.2

59.4

82.2

85.6

90.5

LBAR

24.2

39.1

47.4

53.2

78.7

107.4

147.3

Forecasts

14

14

14

14

14

12

9

Table 3a. NHC official (OFCL) and climatology-persistence skill baseline (OCD5) intensity forecast errors (kt) for Hurricane Felicia east of 140°W. Mean errors for the five-year period 2004-8 are shown for comparison. Official errors that are smaller than the five-year means are shown in boldface type.

Forecast Period (h)

12

24

36

48

72

96

120

OFCL (Felicia)

8.3

13.9

18.1

18.9

11.7

9.3

10.0

OCD5 (Felicia)

10.4

15.1

19.6

18.7

9.1

10.5

13.5

Forecasts

18

18

18

18

18

15

11

OFCL (2004-8)

6.2

10.2

13.3

15.1

17.7

19.0

18.8

OCD5 (2004-8)

7.1

11.5

14.7

16.8

18.9

20.3

20.2

Table 3b. Homogeneous comparison of selected intensity forecast guidance models (in kt) for Hurricane Felicia. Errors smaller than the NHC official forecast are shown in boldface type. The number of official forecasts shown here will generally be smaller than that shown in Table 3a due to the homogeneity requirement.

[1] A digital record of the complete best track, including wind radii, can be found on line at ftp://ftp.nhc.noaa.gov/atcf. Data for the current year's storms are located in the btk directory, while previous year's data are located in the archive directory.

Tropical Depression One-C (TD-1C) developed near 13.5°N 170.0°W, or about 790 nm southwest of Lihue, Hawaii at 0000 UTC 11 August. The west-northwestward moving disturbance from which TD-1C formed was first identified at 1800 UTC 08 August near 10.0°N 159.0°W, or about 725 nm south of Lihue, Hawaii.

TD-1C intensified to a tropical storm at 1200 UTC 11 August, and the Central Pacific Hurricane Center (CPHC) named the system Maka ("Eye" in English). Maka stayed on a west-northwest course attaining peak intensity with maximum sustained winds of 45 knots at 1200 UTC 11 August. Maka weakened to a tropical depression at 0000 UTC 12 August, and remained a tropical depression until the CPHC stopped issuing advisories at 1800 UTC 12 August.

The resultant remnant low moved west, crossing 180°W near 14.3°N shortly after 0600 UTC 13 August. The low turned to the northwest and north over the next several days, reaching 15.3°N 173.1°E at 1800 UTC 15 August. The Joint Typhoon Warning Center (JTWC) upgraded Maka to a tropical storm at that time, and proceeded to downgrade the system to a tropical depression at 0600 UTC 17 August. The last advisory issued by JTWC on Maka was at 0600 UTC 18 August.

b. Synoptic History

Sea surface temperatures were around 28 Deg C and vertical wind shear was insignificant near Maka until 12 August. At low levels, a 1026 hPa subtropical high was centered near 40°N 171°W and an associated subtropical ridge extended from the high north of Maka to near 27°N 163°E. This placed Maka well within a deep layered easterly flow. With the friendly environment, Maka intensified whilst staying on a west-northwest course east of 180°W.

On 12 August, Maka encountered an area of southwesterly shear located south of a middle- and upper-level low pressure system centered near 15.1°N 172.7°W. The shear over a 12 hour period weakened and disorganized Maka resulting in the downgrade to a tropical depression and the cessation of advisories by CPHC. Once west of 180°W, a mid-latitude trough eroded the west end of the subtropical ridge northwest of Maka. The cyclone subsequently turned to the northwest and north toward the weakness in the pressure field.

Figure 1. This infrared satellite image of Maka was taken when the tropical cyclone was at its peak intensity. For reference, the island of Kauai is located in the upper right hand corner of the image.

c. Casualty and Damage Statistics

Maka was never over or near land. Therefore, no tropical cyclone watches or warnings were issued. There were no weather-related casualties or damage reported.

d. Forecast Critique

The genesis of Maka was not well anticipated. The precursor disturbance that developed into Maka was first mentioned in CPHC's Tropical Weather Outlook (TWO) issued at 1800 UTC 08 August. This TWO, as well as succeeding TWOs through 1800 UTC 10 August, only stated that "slow development is possible over the next two days."

GOES and microwave satellite imagery showed that throughout its life span Maka regularly oscillated between being organized and disorganized. Subsequently, the fix data provided by various agencies often had a large spread. This made it difficult to determine an initial position and intensity. In fact, on at least two occasions, the CPHC forecaster was unsure if Maka was a closed circulation at lower levels or a sharp surface trough. Confidence in the official position and intensity as well as the forecast was therefore quite low.

Table 1. Best Track Data for Tropical Storm Maka 11-18 August 2009

Date/Time (UTC)

Latitude (°N)

Longitude (°W)

Pressure (mb)

Wind Speed (kt)

Stage/Notes

08/1800

10.0

159.0

1009

25

Disturbance

09/0000

10.7

160.2

1012

15

"

09/0600

11.2

161.4

1011

20

"

09/1200

11.7

162.5

1011

20

"

09/1800

12.0

163.7

1011

20

"

10/0000

12.3

165.0

1011

20

"

10/0600

12.5

166.3

1011

20

"

10/1200

12.8

167.6

1010

20

"

10/1800

13.1

168.8

1009

25

"

11/0000

13.4

169.7

1009

30

Tropical Depression

11/0600

13.7

170.7

1009

30

"

11/1200

13.9

171.3

1008

35

Tropical Storm

11/1800

14.1

171.8

1008

35

"

12/0000

14.3

172.4

1008

30

Tropical Depression

12/0600

14.4

173.8

1008

30

"

12/1200

14.2

175.3

1008

30

"

12/1800

14.3

176.8

1009

25

"

13/0000

14.4

178.3

1011

25

Disturbance

13/0600

14.3

179.7

1011

25

"

14/0000

13.8

178.6E

1010

20

"

14/0600

13.1

177.3E

1009

20

"

14/1200

13.3

175.9E

1007

20

"

14/1800

13.5

174.6E

1003

25

Tropical Depression

15/0000

13.7

174.0E

1003

25

"

15/0600

14.4

173.2E

1002

30

"

15/1200

14.9

173.1E

1001

30

"

15/1800

15.3

173.1E

997

35

Tropical Storm

16/0000

15.8

173.2E

992

45

"

16/0600

16.0

173.2E

992

45

"

16/1200

16.1

173.2E

992

40

"

16/1800

16.3

173.1E

994

35

"

17/0000

16.3

172.8E

995

35

"

17/0600

16.2

172.6E

998

30

Tropical Depression

17/1200

16.1

172.3E

1000

30

"

17/1800

16.1

172.0E

1000

30

"

18/0000

16.0

171.6E

1000

25

"

18/0600

15.9

171.1E

1006

25

"

Table 2. Track Verification Table entries are track forecast errors, measured in nautical miles. Values in parentheses indicate the number of forecasts. Values in bold represent guidance forecast errors equal to or less than the office CPHC forecast.

Guillermo became a Category 3 hurricane over the open waters of the eastern Pacific Ocean and did not affect land. It persisted as a tropical storm, however, at a relatively high latitude over the central Pacific basin for an unusual amount of time.

a. Synoptic History

Guillermo was spawned by a large, high-amplitude tropical wave that left the west coast of Africa on 26 July. The wave moved westward without significant organization, entering the eastern Pacific on 5 August. Convection increased along the wave axis on 8 August, and an elongated low formed the next day with disorganized banding features noted. Thunderstorms increased markedly near the circulation center late on 11 August, leading to a better-defined circulation by early on 12 August. It is estimated that a tropical depression formed by 1200 UTC 12 August, located about 570 n mi south-southwest of the southern tip of Baja California, and the depression became a tropical storm 12 h later. The "best track" chart of the tropical cyclone's path is given in Figure 1, and the best track positions and intensities are listed in Table 1[1].

Soon after genesis, Guillermo began to intensify, strengthening from a weak tropical storm into a major hurricane in about 48 hours while moving to the west and west-northwest. A banded eye was noted in visible satellite images late on 13 August, and Guillermo became a hurricane early the next day. However, further strengthening was briefly arrested as the banding eye structure transitioned into a central dense overcast pattern, a change which occasionally precedes rapid intensification. Warm water, light shear, and an expanding outflow pattern aloft also probably contributed to a rapid intensification of Guillermo late on 14 August. It became a major hurricane on 15 August, reaching a peak intensity of 110 kt at 1200 UTC while located about 1300 n mi west-southwest of the southern tip of Baja California.

A weakening trend began later that day as sea surface temperatures decreased, and by the time Guillermo crossed into the central Pacific basin very late on 16 August, the cyclone had weakened to an intensity of 65 kt. A gradual decline in intensity continued during the next three days over relatively cool sea-surface temperatures and within an environment of moderate westerly wind shear associated with the flow around a mid- to upper-level trough located to the west of the tropical cyclone. Guillermo headed generally northwestward, well to the north of Hawaii during this period, around a subtropical ridge located to its northeast. By 0600 UTC 17 August, Guillermo weakened to a tropical storm while centered about 740 n mi east of Hilo, Hawaii. Deep convection disappeared near the circulation center later that day, although a QuikSCAT pass over the cyclone at 1648 UTC 17 August revealed winds up to 45 kt within convection far north of the exposed center. By 1800 UTC 19 August, the convection well removed from the center had also vanished, and Guillermo degenerated to a remnant low centered about 550 n mi north of Hawaii.

As the low continued northwestward at about 12 kt, it encountered a frontal zone and developed extratropical characteristics. Deep convection reformed in the northeastern semicircle and, based upon QuikSCAT data, it is estimated that maximum winds increased to 40 kt at 1200 UTC 20 August while the extratropical cyclone was centered about 700 n mi north of Hawaii. The cyclone turned northward as it was steered around the western periphery of the subtropical ridge to its east. Thunderstorms continued in association with the low until around 0600 UTC 21 August, but the system weakened and turned northeastward. Once again reduced to a swirl of low clouds, the low became elongated and was eventually absorbed by an approaching cold front around 1200 UTC 23 August.

b. Meteorological Statistics

Observations in Guillermo (Figs. 2 and 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB), the Central Pacific Hurricane Center, UW-CIMSS intensity estimates using the Advanced Dvorak Technique (ADT) and the Advanced Microwave Sounding Unit (AMSU). Data and imagery from NOAA polar-orbiting satellites, Defense Meteorological Satellite Program (DMSP) satellites, National Aeronautics and Space Administration (NASA) satellites, including TRMM, QuikSCAT, and Aqua, the U.S. Navy WindSat, and the EUMETSAT ASCAT, among other satellites, were also useful in constructing the best track of Guillermo.

The 110-kt peak intensity of Guillermo is based on a blend of satellite estimates from TAFB, SAB, and the ADT technique from UW-CIMSS. Several QuikSCAT passes were helpful for estimating the intensity of Guillermo as it persisted as a tropical storm well north of Hawaii.

There were two ships reporting winds of tropical storm force associated with Guillermo. A ship with the call letters WDC378 measured 38 kt sustained winds on 18 August at 0000 UTC, and 17 h later the ship "Maui" reported 37 kt winds.

c. Forecast and Warning Critique

The genesis of Guillermo was well anticipated. The wave that eventually became Guillermo was introduced in the Tropical Weather Outlook (TWO) about three days before genesis. The genesis forecasts reached the medium (between 30-50%) category about 42 h before formation, although the chance of formation only reached the high (>50% percent) category six hours before genesis.

A verification of NHC official intensity forecasts for Guillermo is given in Table 3a. Official forecast intensity errors were much higher than the mean official errors for the previous five-year period through 72 h and then below the long-term mean afterwards. The rapid strengthening of Guillermo was not well forecast by NHC and caused the large errors. A homogeneous comparison of the official track errors with selected guidance models is given in Table 3b. Although the model errors were also large, the statistical and consensus-based guidance were the best performers with Guillermo.

There were no coastal watches or warnings required for Guillermo and no reports of damage or injuries.

Table 2a. NHC official (OFCL) and climatology-persistence skill baseline (OCD5) track forecast errors (n mi) for Guillermo. Mean errors for the five-year period 2004-8 are shown for comparison. Official errors that are smaller than the five-year means are shown in boldface type.

Forecast Period (h)

12

24

36

48

72

96

120

OFCL (Guillermo)

15.8

24.6

31.7

45.7

83.5

144.2

276.2

OCD5 (Guillermo)

17.8

39.4

73.4

124.2

248.3

358.5

495.7

Forecasts

18

18

18

18

17

13

9

OFCL (2004-8)

31.0

51.7

71.7

90.2

123.6

161.3

201.8

OCD5 (2004-8)

38.4

73.6

111.9

149.1

214.2

261.1

311.5

Table 2b. Homogeneous comparison of selected track forecast guidance models (in n mi) for Guillermo. Errors smaller than the NHC official forecast are shown in boldface type. The number of official forecasts shown here will generally be smaller than that shown in Table 2a due to the homogeneity requirement.

Model ID

Forecast Period (h)

12

24

36

48

72

96

120

OFCL

16.6

25.6

34.0

49.3

87.1

154.5

312.6

OCD5

17.8

40.2

75.3

126.2

250.2

364.6

507.3

GFSI

21.1

33.6

46.4

57.2

80.4

105.8

214.0

GHMI

20.9

35.4

46.1

66.1

77.2

61.1

226.1

HWFI

20.8

47.2

72.2

92.6

93.9

83.1

144.7

NGPI

18.7

39.6

74.8

126.5

240.0

313.4

385.5

FSSE

14.4

28.9

43.4

59.2

83.8

118.3

246.5

TVCN

15.0

25.4

40.0

58.7

91.1

138.6

254.3

TVCC

11.5

22.7

30.1

57.0

92.2

187.3

383.6

LBAR

30.8

76.0

126.5

185.1

354.1

656.8

1034.5

BAMD

27.2

64.8

106.6

152.6

299.6

577.6

832.3

BAMM

29.7

60.0

89.4

116.7

175.4

266.5

386.6

BAMS

30.1

50.1

57.2

69.5

99.5

121.1

169.9

Forecasts

16

16

16

16

15

11

7

Table 3a. NHC official (OFCL) and climatology-persistence skill baseline (OCD5) intensity forecast errors (kt) for Guillermo. Mean errors for the five-year period 2004-8 are shown for comparison. Official errors that are smaller than the five-year means are shown in boldface type.

Forecast Period (h)

12

24

36

48

72

96

120

OFCL (Guillermo)

8.6

14.4

18.6

22.5

19.1

12.7

8.3

OCD5 (Guillermo)

8.4

15.2

20.9

25.1

18.3

11.2

4.4

Forecasts

18

18

18

18

17

13

9

OFCL (2004-8)

6.2

10.2

13.3

15.1

17.7

19.0

18.8

OCD5 (2004-8)

7.1

11.5

14.7

16.8

18.9

20.3

20.2

Table 3b. Homogeneous comparison of selected intensity forecast guidance models (in kt) for Guillermo. Errors smaller than the NHC official forecast are shown in boldface type. The number of official forecasts shown here will generally be smaller than that shown in Table 3a due to the homogeneity requirement.

Model ID

Forecast Period (h)

12

24

36

48

72

96

120

OFCL

9.4

14.7

19.4

22.2

14.3

8.6

7.9

OCD5

8.8

14.9

21.0

24.0

13.3

6.9

5.0

DSHP

7.8

10.4

14.9

17.3

13.5

9.5

7.7

LGEM

8.8

13.1

18.1

19.7

12.1

7.2

8.0

GHMI

9.6

17.6

24.5

24.7

19.3

10.7

9.0

HWFI

10.8

15.2

19.9

22.1

18.1

12.6

7.9

FSSE

9.9

15.6

20.1

21.1

14.8

7.7

7.7

ICON

8.8

13.5

17.9

19.7

13.9

6.8

5.0

IVCN

8.7

13.9

17.9

19.5

13.1

5.9

5.6

Forecasts

16

16

16

16

15

11

7

[1] A digital record of the complete best track, including wind radii, can be found on line at ftp://ftp.nhc.noaa.gov/atcf. Data for the current year's storms are located in the btk directory, while previous years' data are located in the archive directory.

Hilda was a tropical storm that spent most of its existence in the central North Pacific basin, passing well to the south of Hawaii.

a. Synoptic History

Hilda appears to have been spawned by a tropical wave that crossed Central America on 13 August. This wave moved westward over the eastern North Pacific for several days with little or no indications of development. By 18 August, deep convection associated with the system began to show some signs of organization, and the wave spawned a westward-moving low-level circulation around 1200 UTC 21 August. Thunderstorm activity associated with this circulation was not sufficiently well organized, however, to designate the formation of a tropical cyclone until 1200 UTC 22 August when it is estimated that a tropical depression formed while centered a little over 1100 n mi east-southeast of the Big Island of Hawaii. Although situated in an environment of northeasterly vertical shear, the cyclone was able to strengthen a little, and satellite imagery and scatterometer data indicate that it became a tropical storm some six hours after genesis. The "best track" chart of Hilda's path is given in Fig. 1, with the wind and pressure histories shown in Figs. 2 and 3, respectively. The best track positions and intensities are listed in Table 1[1].

Hilda was located to the south of the eastern edge of a subtropical ridge over the central North Pacific, and the associated steering current moved the storm on a westward heading at 8-9 kt. Strengthening was limited by persistent northeasterly shear, and Hilda crossed into the central North Pacific basin around 1200 UTC 23 August with an estimated intensity of 40 kt. The moderate shear continued over the cyclone, but Hilda was able to intensify a little more, reaching its peak intensity of 55 kt by 0600 UTC 24 August, when it was located about 740 n mi southeast of the Big Island of Hawaii. Lumbering generally westward to the south of a mid-level ridge for the next couple of days, Hilda encountered an environment that was less conducive for strengthening. Early on 25 August, despite stronger Dvorak estimates, passive microwave imagery reveals that convective coverage had decreased, suggesting the storm had begun a weakening trend. A QuikSCAT overpass from later that day confirms Hilda had weakened, to about 45 kt by 1800 UTC 25 August. Hilda's convective structure continued to deteriorate, and the cyclone eventually weakened to a tropical depression by 0000 UTC 27 August while centered about 430 n mi south-southeast of the Big Island of Hawaii. The depression produced persistent but limited convection for a couple of more days as it continued westward, well to the south of Hawaii, and by 1800 UTC 28 August the cyclone degenerated to a remnant low. Steered by the low-level trade wind flow, the remnant circulation headed west-northwestward for the following three days, and finally dissipated late on 31 August about 1100 n mi west-southwest of Honolulu.

b. Meteorological Statistics

Observations in Hilda (Figs. 2 and 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Central Pacific Hurricane Center (PHFO), and the Joint Typhoon Warning Center (JTWC) the Satellite Analysis Branch (SAB). Data and imagery from NOAA polar-orbiting satellites, the NASA Tropical Rainfall Measuring Mission (TRMM), the NASA QuikSCAT, and Defense Meteorological Satellite Program (DMSP) satellites, among others, were also useful in constructing the best track of Hilda.

The cyclone's peak intensity of 55 kt on 24 August is based on a consensus of subjective Dvorak estimates. Several QuikSCAT overpasses were useful in estimating Hilda's strength both before and after the time of peak intensity.

No ship reports of winds of tropical storm force associated with Hilda have been received.

c. Casualty and Damage Statistics

There were no reports of damage or casualties associated with Hilda.

d. Forecast and Warning Critique

The area of disturbed weather that eventually developed into Hilda was first mentioned in the National Hurricane Center's (NHC's) Tropical Weather Outlook (TWO) at 1800 UTC 20 August, a little less than two days prior to genesis. This system was initially assigned a low (less than 30 percent) chance of tropical cyclone formation over the ensuing 48 h. In the TWO issued 24 h before genesis, the formation probability was increased to medium (30 to 50 percent chance), and it was set to high (greater than 50 percent chance) in the TWO issued 18 h prior to genesis.

A verification of NHC official intensity forecasts for Hilda is given in Table 3. At most forecast intervals, the mean NHC intensity forecast errors were lower than the mean official errors for the previous five-year period. The mean climatology-persistence intensity forecasts for this tropical cyclone were below the previous five-year means at all forecast intervals, which suggests that Hilda's intensity was somewhat easier to forecast than average.

No watches or warnings were issued for Hilda.

Table 1. Best track for Tropical Storm Hilda, 22-28 August 2009.

Date/Time (UTC)

Latitude (°N)

Longitude (°W)

Pressure (mb)

Wind Speed (kt)

Stage

21 / 1200

13.5

133.0

1009

25

low

21 / 1800

13.5

133.8

1008

25

"

22 / 0000

13.6

134.6

1008

25

"

22 / 0600

13.6

135.5

1008

25

"

22 / 1200

13.5

136.4

1006

30

tropical depression

22 / 1800

13.5

137.3

1005

35

tropical storm

23 / 0000

13.5

138.1

1005

35

"

23 / 0600

13.6

138.9

1003

40

"

23 / 1200

13.8

140.0

1003

40

"

23 / 1800

13.9

141.2

1000

45

"

24 / 0000

14.0

142.5

998

50

"

24 / 0600

14.2

143.6

995

55

"

24 / 1200

14.5

144.6

995

55

"

24 / 1800

14.8

145.5

995

55

"

25 / 0000

14.9

146.4

997

50

"

25 / 0600

14.7

147.2

997

50

"

25 / 1200

14.4

147.9

997

50

"

25 / 1800

14.1

148.6

999

45

"

26 / 0000

13.8

149.1

1001

40

"

26 / 0600

13.5

149.6

1002

40

"

26 / 1200

13.3

150.2

1003

40

"

26 / 1800

13.2

150.8

1004

35

"

27 / 0000

13.3

151.4

1005

30

tropical depression

27 / 0600

13.6

152.2

1005

30

"

27 / 1200

13.7

153.1

1006

30

"

28 / 0000

13.7

155.3

1006

30

"

28 / 0600

13.8

156.5

1006

30

"

28 / 1200

13.9

157.8

1006

30

"

28 / 1800

14.0

159.2

1007

25

remnant low

29 / 0000

14.2

160.8

1007

25

"

29 / 0600

14.6

162.4

1007

25

"

29 / 1200

15.1

163.9

1007

25

"

29 / 1800

15.3

165.5

1007

25

"

30 / 0000

15.5

167.0

1007

25

"

30 / 0600

15.7

168.7

1007

25

"

30 / 1200

15.8

170.4

1007

25

"

30 / 1800

16.0

172.1

1007

25

"

31 / 0000

16.2

173.8

1007

25

"

31 / 0600

16.4

175.2

1008

20

"

31 / 1200

16.6

176.4

1008

20

"

31 / 1800

16.8

177.4

1008

20

"

1 / 0000

dissipated

24 / 0600

14.2

143.6

995

55

minimum pressure

Table 2. NHC official (OFCL) and climatology-persistence skill baseline (OCD5) track forecast errors (n mi) for Tropical Storm Hilda, 22-28 August 2009. Mean errors for the five-year period 2004-8 are shown for comparison. Official errors that are smaller than the five-year means are shown in boldface type.

Forecast Period (h)

12

24

36

48

72

96

120

OFCL

27.5

58.0

86.5

91.1

99.9

106.2

123.6

OCD5

30.6

53.2

76.8

76.6

120.2

201.0

238.9

Forecasts

5

5

5

5

5

5

5

OFCL (2004-8)

31.0

51.7

71.7

90.2

123.6

161.3

201.8

OCD5 (2004-8)

38.4

73.6

111.9

149.1

214.2

261.1

311.5

Table 3. NHC official (OFCL) and climatology-persistence skill baseline (OCD5) intensity forecast errors (kt) for Tropical Storm Hilda, 22-28 August 2009. Mean errors for the five-year period 2004-8 are shown for comparison. Official errors that are smaller than the five-year means are shown in boldface type.

[1] A digital record of the complete best track, including wind radii, can be found on line at ftp://ftp.nhc.noaa.gov/atcf. Data for the current year's storms are located in the btk directory, while previous years' data are located in the archive directory.

Tropical Depression (TD) Two-C originated from a west-moving trade wind disturbance in the extreme southwestern portion of the central Pacific basin. Despite atmospheric and oceanic conditions that appeared to be conducive for further development, the depression never attained tropical storm intensity, as it tracked west across the date line out of the Central Pacific Hurricane Center's (CPHC) Area Of Responsibility (AOR), and into the western Pacific basin, before eventually dissipating.

CPHC started tracking a trough in the trade wind easterlies at 0600 UTC 26 August, about 925 n mi southwest of Honolulu, Hawaii near 12°N 171°W. Near 1800 UTC 27 August, satellite imagery revealed that the low-level trough axis appeared to be developing a closed low-level circulation, and deep convection began to increase near the core of this low. It is estimated that a tropical depression formed around 1200 UTC 28 August, while centered about 1125 n mi west-southwest of Honolulu, Hawaii near 14.5°N 176.3°W. The best track positions and intensities are listed in Table 1.

The depression initially moved westward at 6-7 kt to the south of the subtropical ridge, while maintaining sporadic convection near the low level circulation center. The depression accelerated toward the west after crossing the International Date Line, and this appeared to correspond to a weakening system, increasingly influenced by the steering in the lowest levels of the atmosphere. The system was completely devoid of deep convection by 0600 UTC 30 August, at which time the Joint Typhoon Warning Center (JTWC) indicated a weakening system, lowering the maximum sustained winds to 25 kt. The system continued to be classified as a 25 kt depression at 1200 UTC 30 August, but was deemed to have weakened to a disturbance by 1800 UTC 30 August. A low cloud swirl was tracked westward by JTWC for several days, after which the remnant weak circulation dissipated well west of CPHC's AOR.

The genesis of Tropical Depression Two-C was not well anticipated, although it's pre-existing low-level vorticity center was being tracked by CPHC for several days, with the disturbance first mentioned in CPHC's Tropical Weather Outlook issued 0200 UTC 25 August. CPHC's experimental 48 hour tropical cyclogenesis probabilities indicated a "low" probability (less than 30%) that the incipient Two-C would develop into a tropical cyclone until the day that the disturbance began to show improved organization. No coastal tropical cyclone watches or warnings were issued in association with Two-C, as it remained over water and away from any significant or populated Pacific islands.

Figure 1. Visible image of tropical depression Two-C at 2330 UTC 28 August 2009, as it approaches the International Date Line. (Image courtesy Naval Research Laboratory)

Neki was the final tropical cyclone and only category three hurricane within the Central Pacific in 2009. After developing south of the main Hawaiian Islands, Neki moved to northwest, then turned to the north, passing through the Papahanaumokuakea Marine National Monument as a tropical storm and impacting French Frigate Shoals and Necker Island. Neki degenerated into a remnant low over the open waters of the Central Pacific.

a. Synoptic History

Neki originated within a broad, persistent, approximately west-to-east oriented near-equatorial trough spanning a vast portion of the Central Pacific. This surface trough had been a prominent feature in the Central Pacific since 11 October, and weak disturbances had been identified within the trough as early as 15 October. By 0000 UTC on 18 October, weakly curved bands of deep convection began to focus to the north and south of the western terminus of the trough, forming a rather large gyre not typically observed in the Central Pacific.

Shortly after 1200 UTC on 18 October, deep convection started to develop and organize around an elongated low-level center near the middle of the gyre, and it was estimated that a tropical depression formed around 1800 UTC on 18 October about 635 n mi south of South Point on the island of Hawaii. Neki was moving toward the west northwest at less than 10 kt, steered by deep easterly flow to the south of a subtropical ridge. The "best track" chart of Neki's track is given in Fig. 1, and the best track positions and intensities are listed in Table 1.

Deep convection gradually consolidated around the low-level center through early 19 October, and it was estimated that the system reached tropical storm intensity by 1200 UTC on 19 October. The large circulation encompassing the tropical cyclone was slow to develop and break away from the near-equatorial surface trough where it originated, and QuikSCAT data, which detected an area of 35 kt winds near the low-level center at 0426 UTC and at 1709 UTC, provided critical information. During the last half of 19 October, Neki took a turn to the northwest as the subtropical ridge north of the system was being rapidly eroded by an approaching upper level trough to the northwest.

Organization improved rapidly on 20 October as Neki continued to move to the northwest around 15 kt toward a forming weakness in the subtropical ridge, and it was estimated that Neki became a hurricane by 0000 UTC on 21 October while centered 545 n mi of Honolulu and 290 n mi east southeast of Johnston Atoll. An intermittent banding eye had been developing late in the day on 20 October, and an Aqua AMSR-E pass at 0006 UTC on 21 October (Fig. 2) confirmed the presence of a partial eye wall. In an environment of low vertical wind shear and sea surface temperatures of 28 degrees Celsius, Neki continued to rapidly intensify through 21 October, reaching a peak intensity of 110 kt at 0000 UTC on 22 October. Around this time, Neki assumed a due north heading as a broad, North Pacific upper level trough steadily eroded ridging at the surface and aloft to the north, weakening the steering flow and leading to a decrease in the forward speed to less than 10 kt. As Neki moved to the north on 22 October, a slow weakening process began as increasing southwest winds aloft associated with the nearby upper level trough restricted outflow in the western quadrant and created vertical wind shear up to 25 kt according to analyses from the Cooperative Institute for Meteorological Satellite Studies/University of Wisconsin-Madison (UW-CIMSS). Continued interaction with the upper level trough prompted a turn to the northeast and led to steady weakening as vertical wind shear increased on 23 October.

Neki weakened to a tropical storm around 1800 UTC on 23 October as the system neared the Papahanaumokuakea Marine National Monument (PMNM). Strong southwesterly vertical wind shear slowly weakened Neki on 24 October as it passed through the PMNM coming within 60 n mi of French Frigate Shoals at 0000 UTC and within 11 n mi of uninhabited Necker Island at 0600 UTC. Neki's advance to the northeast was abruptly halted on 25 October as a transient high passed to the north, likely causing Neki to undertake an anticyclonic loop between 0600 and 1800 UTC. Neki resumed a slow motion to the northwest on 26 October as the surface high passed to the east. Continued westerly vertical wind shear caused the low-level circulation to decouple from the circulation aloft, and Neki became a tropical depression around 1800 UTC on 26 October. Thereafter, the low level center emerged to the northwest of an area of deep convection and quickly became indistinguishable as an elongated and rapidly dissipating surface trough 350 n mi southeast of an approaching cold front. The system dissipated by 0600 UTC on 27 October.

The estimated peak intensity of 110 kt at 0000 UTC on 22 October is based on an average of the subjective satellite-based Dvorak technique intensity estimates as well as peak objective Dvorak intensity estimates.

There were no ship reports of tropical storm force winds in association with Neki.

c. Casualty and Damage Statistics

There were no reports of damage or casualties associated with Neki. However, due to the extreme vulnerability of the low-lying islands and atolls within the PMNM, evacuations were conducted at two locations. Ten personnel were evacuated from Tern Island within French Frigate Shoals by a United States Coast Guard C-130 at approximately 2230 UTC on 21 October. To the northwest at Laysan Island, several individuals were removed by NOAA R/V Sette at approximately 0130 UTC on 22 October.

d. Forecast and Warning Critique

The genesis of Neki was fairly well anticipated. Neki originated within a broad, persistent, approximately west-to-east oriented near-equatorial trough that had been a prominent feature in the Central Pacific since 11 October. Disturbances within this trough were first mentioned in the Tropical Weather Outlook at 0200 UTC on 15 October.

A verification of CPHC official track forecasts is provided in Table 2. Average official track errors for Neki (with the number of cases in parentheses) were 41 (32), 69 (30), 103 (28), 149 (26), 265 (22), 393 (18), and 436 (14) n mi for the 12, 24, 36, 48, 72, 96, and 120 hour forecasts, respectively. Neki's erratic track proved difficult to forecast, causing errors in the official forecast and nearly all of the model guidance to be much higher than the CPHC long term average through 48 hours and nearly double the CPHC long term average beyond 48 hours. The GFSI, HWFI, GFDI, and the GUNA, TCON, and TVCN had average errors lower than the official forecasts during most time periods.

Average official intensity errors (Table 3) were 7, 11, 14, 16, 22, 26, and 34 kt for the 12, 24, 36, 48, 72, 96, and 120 hour forecasts, respectively. While CPHC intensity forecasts had lower errors than the GFSI, NGPI, HWFI, and GFDI for nearly all time periods, CPHC intensity forecasts were out-performed by DSHP and LGEM beyond 24 hours and by the ICON consensus model beyond the 12 hour forecast time period.

Watches and warnings associated with Neki are given in Table 4, while a map displaying the affected areas is provided in Figure 3. A hurricane watch was issued for the PMNM from French Frigate Shoals to Maro Reef to Lisianski Island at 0900 UTC on 21 October, approximately 45 hours prior to the 34 kt wind radius reaching the area, and was expanded southeastward from French Frigate Shoals to Nihoa Island at 1500 UTC on 21 October, approximately 39 hours prior to the 34 kt wind radius reaching the area. A hurricane warning was issued from Nihoa Island to French Frigate Shoals to Maro Reef at 2100 UTC on 21 October, approximately 33 hours prior to the 34 kt wind radius reaching the area.

A hurricane watch was issued for Johnston Island at 0300 UTC on 21 October, but no warnings were issued for this location.

Table 1. Best track for Hurricane Neki, 18 - 27 October 2009.

Date/Time (UTC)

Latitude (°N)

Longitude (°W)

Pressure (mb)

Wind Speed (kt)

Stage

18 / 1800

8.4

156.2

1008

25

tropical depression

19 / 0000

8.5

156.5

1007

30

"

19 / 0600

8.9

157.3

1007

30

"

19 / 1200

9.4

158.0

1006

35

tropical storm

19 / 1800

10.3

159.1

1006

35

"

20 / 0000

11.1

160.4

1006

35

"

20 / 0600

11.9

161.7

1005

40

"

20 / 1200

12.8

162.8

1001

55

"

20 / 1800

13.9

163.7

996

60

"

21 / 0000

15.0

164.8

992

65

hurricane

21 / 0600

15.9

165.7

985

75

"

21 / 1200

16.6

166.4

975

90

"

21 / 1800

17.6

166.6

960

100

"

22 / 0000

18.3

166.7

950

110

"

22 / 0600

19.0

166.7

956

105

"

22 / 1200

19.7

166.6

965

100

"

22 / 1800

20.4

166.4

970

90

"

23 / 0000

21.1

166.2

975

85

"

23 / 0600

21.9

165.9

980

80

"

23 / 1200

22.5

165.6

990

70

"

23 / 1800

22.9

165.4

995

60

tropical storm

24 / 0000

23.3

165.2

998

55

"

24 / 0600

23.6

164.9

999

55

"

24 / 1200

24.0

164.4

1001

50

"

24 / 1800

24.5

164.0

1001

50

"

25 / 0000

24.7

163.9

1001

50

"

25 / 0600

24.7

163.9

1002

50

"

25 / 1200

24.6

164.0

1003

45

"

25 / 1800

24.7

164.2

1003

45

"

26 / 0000

24.8

164.7

1006

40

"

26 / 0600

25.3

164.9

1008

35

"

26 / 1200

25.9

165.0

1009

35

"

26 / 1800

27.1

165.6

1010

30

tropical depression

27 / 0000

28.8

165.3

1010

30

"

22 / 0000

18.3

166.7

950

110

minimum pressure/ maximum wind

Table 2. Track forecast evaluation for Hurricane Neki, 18 - 27 October 2009. Forecast errors (n mi) are followed by the number of forecasts in parentheses. Errors smaller than the CPHC official forecast are shown in bold.

Forecast Technique

Forecast

Period

12-hr

24-hr

36-hr

48-hr

72-hr

96-hr

120-hr

OFCL

41 (32)

69 (30)

103 (28)

149 (26)

265 (22)

393 (18)

436 (14)

CLP5

54 (32)

106 (30)

166 (28)

225 (26)

361 (22)

535 (18)

781 (14)

BAMD

51 (32)

95 (30)

154 (28)

231 (26)

390 (22)

605 (18)

718 (14)

BAMM

38 (52)

61 (30)

87 (28)

121 (26)

210 (22)

407 (18)

511 (14)

BAMS

54 (32)

89 (30)

127 (28)

164 (26)

228 (22)

327 (18)

461 (14)

GFSI

45 (32)

64 (29)

92 (28)

126 (26)

216 (22)

360 (18)

413 (13)

NGPI

46 (31)

80 (29)

110 (27)

138 (25)

204 (21)

314 (17)

467 (13)

HWFI

31 (32)

49 (30)

78 (28)

114 (26)

202 (22)

371 (18)

415 (14)

GFDI

33 (32)

54 (30)

84 (28)

131 (26)

218 (22)

378 (18)

438 (14)

GUNA

35 (30)

62 (27)

95 (26)

131 (24)

218 (20)

356 (16)

458 (8)

TCON

33 (30)

56 (27)

88 (26)

124 (24)

212 (20)

358 (16)

435 (8)

TVCN

36 (32)

60 (30)

87 (28)

119 (26)

198 (22)

337 (18)

429 (14)

Table 3. Intensity forecast evaluation for Hurricane Neki, 18 - 27 October 2009. Forecast errors (kt) are followed by the number of forecasts in parentheses. Errors smaller than the CPHC official forecast are shown in bold.